How much is a large trade size to the market

Same here; personally I don’t use such more than 1$ trading lot size. Because, money management is very much important parameter for my live trading.

I’m not necessarily disagreeing, but even though FX is a decentralized market, the average price within a certain tolerance is not - in other words, the price that a trader sees trading with bucket shop X is roughly the same as another trader with giant broker Y. How can any broker offset a toxic trade for more than a few pips or minutes at a time?

Risk is pretty important too.

Yes, both are important! We need to make our trading plan according to the money management as well as risk management policies.